Potent Antioxidative Isoflavones Isolated from Soybeans Fermented with Aspergillus saitoi

Abstract

  Two potent antioxidative isoflavones were isolated from soybeans fermented with Aspergillus saitoi by silica gel column chromatography and preparative HPLC, using ODS column, or in addition, Toyopearl HW-40 column chromatography. The purified AS-13 and AS-9B compounds were identified as 8-hydroxydaidzein (8-OHD) and 8-hydroxygenistein (8-OHG), respectively, by MS, and ¹H-NMR, ¹³C-NMR and HMBC spectra. These isoflavones, which have an o-dihydroxy structure between the 7- and 8-position, each exhibited significantly stronger antioxidative activity than daidzein and genistein in both oil and lipid/aqueous systems. Furthermore, the antioxidative activity and the content of each isoflavone analog in soybeans with different fermentation periods were investigated. It is suggested from these results that AS-13 and AS-9B were produced from daidzein and genistein, respectively, by hydroxylation at the 8-position of each isoflavone structure. In addition, it is concluded that these isoflavones were also the principal antioxidants in potent antioxidative soybeans fermented with A. saitoi.